This invention relates to electrostatic sprayers, and more particularly to an ignition and fire suppressing system for such electrostatic sprayers.
Electrostatic spraying devices are widely used for the deposition of coating materials on articles to be finished or coated. Such devices usually include a sprayer from which a coating material is issued in an atomized form. Conduits connect an atomizing gas and the coating material to the sprayer. a high voltage power supply is also connected to the sprayer for charging the atomized coating material particles so that electrostatic forces will aid in attracting the coating material to the grounded article being finished. Such sprayers may be mechanically mounted and automatic or be hand held for manual operation.
Extremely high voltages, in the range of 60,000 to 120,000 volts, are required for imparting an adequate charge to the atomized material for successful and efficient deposition of spray coating materials by electrostatic means. Such high voltages present a problem of sparks or arcs which may occur between the electrostatic sprayer and the article to be coated or other nearby grounded objects. this arcing problem becomes critical where the atomized coating material or its organic carrying solution is extremely flammable. Ignition of these flammable materials could cause an explosion, a spray pattern fire about the sprayer or a fire on the article being coated.
Arc-detecting circuitry, which senses prospective ionizing sparks or arcs and shorts or turns off the high voltage power supply to avoid such hazardous conditions are repeatedly demonstrated in the prior art, U.S. Pat. Nos. 4,075,677, 3,894,272, 3,875,892, 4,402,030 and 3,809,955 disclose circuitry of that sort. Such circuitries typically sense a current surge in the high voltage power supply which is indicative of prospective arcs or sparks and either disconnect the high voltage power supply from the charging electrodes of the sprayer, or electrically connect the high voltage to ground.
Despite arc-detection circuitry, arcs and resultant fires do occur on occasion. In the past if a fire has occurred, conventional extinguishing means have typically been used. that is, hand-held fire extinguishers are utilized, or a switch or sensor for a fixed fire extinguishing system is activated. Such extinguishing means are timed to activate and put out the fire and often use chemicals which may contaminate the working area or articles to be coated.